First off, I don't understand "metric" temperature.
Is -10c cold?
As for your truck's performance, I hope it's normal because mine acts that way also. I block about 1/3 of the radiator when it's below 15-20F, and about 1/2 when it's below 0F. Helps quite a bit. Last October in the mountains it was about 6 or 8F one morning I headed out to trout fish and I got delayed with some mountain road construction and about froze sitting at idle for several minutes. Didn't have the radiator blocked yet, and was wishing I did.
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Our Raptor RV
2006 F350 CC LWB Dually XLT Oxford white manual 4x4 6.0 PSD 6 speed. 4.10 LS front and rear, Built May05. 4" turbo back, 100gal aux fuel tank. A real pig from a stop, but give me 10' and she'll lite'em up.
150K miles, 12 injectors, EGR cooler, Fuel pump, 8glow plugs, GPCM, FICM rebuilt FoMoCo longblock under 7/200 warranty.
